The common keyboard used for a computer always makes sounds when the keys are tapped, but these sounds often bother users who need quiet. In addition, some people use their keyboards in the office during lunchtime, and these sounds could disturb other people who are trying to take a break. Please refer to FIG. 1, which is a cross-sectional view of a conventional keyboard structure. A keyboard 10 includes a key top 11, a butting column 12 (which may also be referred to as a crater), a central post 13, two protrusions 14 moving within the butting column 12 in a balanced manner, left and right side portions 15, left and right top portions 16 (i.e., a stopping piece, which has a regular height/thickness (DP) of 1.4 mm), a bottom portion 17, a conductive membrane 171, a silicone rubber dome 18 and two outer portions 19, wherein the outer portions 19 are embedded below a keyboard surface 101 of the keyboard 10 with an embedded depth (ED) of 2 mm. Each of the two surrounding parts 181 of the silicone rubber dome 18 around the central post 13 has a height (HT) of 0.8 mm.
The reason why the existing keyboard 10 makes noise can be understood from FIG. 1. It is usually nothing more than the sounds caused by the side portions 15 hitting an urging surface 161 of the top portion 16 and the protrusions 14 hitting the bottom portion 17 when the key top 11 is pressed down (of course, if the central post 13 pushes the silicone rubber dome 18 to hit the conductive membrane 171, the protrusions 14 no longer hit the bottom portion 17, and a clicking sound caused by hitting the bottom portion 17 does not occur), and the sound caused by the protrusions 14 hitting a stopping surface 162 of the top portion 16 after the central post 13 of the key top 11 is the rebound of the silicone rubber dome 18 (where the stopping surface 162 prevents the protrusions 14 from disengaging and falling off). That is to say, when pressing down the keys of the keyboard 10, the sounds are made by the key top 11 hitting the bottom portion 17 (hereinafter abbreviated as ‘site A’), the urging surface 161 (hereinafter abbreviated as ‘site B’) and the stopping surface 162 (hereinafter abbreviated as ‘site C’).
Therefore, the objective is to eliminate the problem of clicking sounds made at sites A, B and C when pressing down the keys of the keyboard. The inventor of the present application endeavored in experiments, tests and research, and has finally created a keyboard device, where clicking sounds made at sites A, B and C not only effectively disappear when pressing the keys, but it also makes typing more fluent. In other words, the problems to be solved by the present invention are, when using the keyboard, how to overcome the problem of clicking sounds made at site C (so as to make the key top rebound soundlessly), site A and site B. The summary of the present invention is described below.